1. Field of the Invention
The present invention relates to a method and apparatus for assuring combustion of fuel injected in a combustion chamber of an internal combustion engine.
2. Description of the Related Art
Diesel engines of both the 2-cycle and 4-cycle types have enormous acceptance throughout the world and they are also the types of engines that would benefit the most from application of the present invention. When engine longevity and fuel economy are more important than the power-to-weight ratio or the ability to operate through a wide range of engine speeds, diesel fueled engines are ideal.
Both Sir Harry R. Ricardo in his book The High Speed Internal Combustion Engine and Charles Fayette Taylor in his two volume set The Internal Combustion Engine in Theory and Practice states that once the piston in a diesel engine goes more than about one third of the way down on its power stroke, the flame in the combustion chamber goes out. Although diesel engines have much better fuel economy than that of gasoline engines of the same power output, the diesel engines fuel economy is still constrained by the time needed for complete combustion.
In an engine that is dependent upon the heat of compression to initiate and maintain combustion, the relatively slow process of fuel injection, mixing of the fuel with the air, and the combustion itself must take place before the flame goes out as the piston travels past the first third of its power stroke.
The primary cause of diesel engine pollution is its dependence upon the heat of compression inside the combustion chamber for initiation and maintenance of the combustion process. Regardless of engine rpm, the actual time (not degrees of crank rotation) that it takes for the fuel and air to mix and burn is relatively long because diesel fuel is notoriously hard to ignite and keep burning.
This difficulty of ignition can be demonstrated from putting out a match by dipping it in a cup of diesel fuel. This can also be demonstrated by placing a conventional spark plug in the fuel spray pattern of a fuel injector. When diesel fuel is injected into a spark plug's gap, the spark is extinguished there and the spark then takes place outside of the combustion chamber by taking a path outside of the spark plug ceramic insulator from its high voltage terminal to its threaded base. The difficulty of igniting diesel fuel with a spark plug is demonstrated further by the absence of spark assisted diesel engines from the market.
For the heat of compression in a diesel engine to be sufficient for the initiation of the combustion process, the compression ratio must be relatively high. In some engines this compression ratio is as high as 18 to 1. This results in a very high combustion chamber pressure even before the fuel is injected into the combustion chamber. Since combustion starts at an already high pressure, the combustion chamber temperature and pressure quickly increase to the point where the oxygen and nitrogen that are naturally present in air combine to create oxides of nitrogen (also referred to as NOx). Pollution from these oxides of nitrogen is the primary cause of acid rain, photo-chemical smog and a host of other very serious ecological and health problems.
The actual time needed for complete combustion to take place in a diesel engine is the primary cause of the other main type of pollutant emissions from diesel engine operation.
Any fuel that is not combusted or partially combusted as the piston goes down past a third of the way down its power stroke never gets burned. This problem becomes worse if the engine is operating at full speed (as measured in revolutions per minute) and/or at full power. Any partially or not combusted fuel left in the combustion chamber when the piston travels past the first third of the power stroke then exits through the exhaust port as unburned hydrocarbons, partially combusted hydrocarbons, and particulate matter, all of which together are more commonly referred to as smoke. Making this pollution even worse is the fact that the NOx created reacts with the water naturally present in engine exhaust to make nitric acid. This nitric acid then in turn reacts with the smoke to create a carcinogenic stew of truly unhealthy and dangerous chemicals. These chemicals are so harmful that under present Federal law, they could not be accepted by a landfill in the form of solid or liquid waste.
Until very recently, the only "pollution control device" that was installed on diesel engines in the United States was an engine speed governor. The function of this governor was to make sure that enough time was allowed during the power stroke so that sufficient combustion took place prior to the piston traveling past the first third of its power stroke in order to prevent the creation of visible smoke by the engine. All too often truck operators disable this governor so that they could squeeze a little extra power out of their engine while going up hill or passing other vehicles. Their ecological irresponsibility is evident from the enormous black clouds belching out of their exhaust stacks and left in their wake.
The Environmental Protection Agency (henceforth referred to as the EPA) has allowed until recently for diesel engines to be "grand-fathered" out of earlier pollution control regulations.
This was done for three reasons:
1. Diesel engines get much better fuel economy than gasoline engines of the same power output; PA0 2. The currently accepted theory of operation for diesel engines did not allow for major changes in design that could be applied in a cost-effective manner; and PA0 3. There was not any readily available alternative type of engine design that could perform the jobs currently done by diesel engines. PA0 1. Assuring the complete combustion of the fuel inside the combustion chamber, when and where it does the work rather than wasting it by allowing un-combusted and partially combusted fuel to escape out through the exhaust port; PA0 2. Avoiding the endothermic chemical reaction that creates oxides of nitrogen (NOx); PA0 3. Reducing pumping losses when an engine equipped with the present invention is operating at less than full power. This is especially important for automotive diesels since they spend much more of their operating time cruising at partial power or idling than they do at full power. The only time that an automotive diesel engine is run at full power is when the vehicle is either going up hill or being accelerated. Since the present invention assures combustion regardless of pressure, pumping losses can be reduced by throttling the air entering the intake manifold; PA0 4. Improving the effective ratio of expansion during the engine power stroke. An engine equipped with the present invention has the fuel burn completed earlier in its power stroke, thus improving the effective ratio of expansion which improves thermal efficiency. PA0 1. The mechanically defined compression ratio can be reduced without unacceptably degrading performance; PA0 2. The timing of the initiation of fuel injection can be retarded in terms of degrees of crankshaft rotation without unacceptably degrading performance; PA0 3. The rate of injection can be controlled by a closed-loop feedback system such as an engine management computer responding in real-time to combustion chamber pressure and temperature. Since the present invention assures combustion of the fuel upon injection, it becomes possible to regulate the rate of injection so that the temperature and pressure inside the combustion chamber will be kept below the threshold above which NOx is formed.
Over the last three decades this has resulted in a slower pace of design advancement for diesel engines, especially for pollution reduction, when compared to design advancements made on gasoline engines. As a result diesel engine design has improved only incrementally over the last thirty years without major reductions in pollutant emission levels.
During the same period of time, an outstanding job of cleaning up gasoline engines and other industrial sources of air pollution took place. However, air pollution created by diesel engines has remained about the same for a given amount of power produced. This caused the relative percentage of air pollution produced by diesel engines to become the primary cause of air pollution in the US.
In response to this, the EPA started looking into ways to reduce diesel engine pollutant emissions. They mentioned several possible means to achieve this in a fact sheet issued in October 1995 (EPA 420-F-95-009a) that included "after treatment" such as catalytic converters, fuel delivery control systems, air intake strategies, and changing diesel fuel formulations. This was followed in August 1998 by a Regulatory Announcement--New Standards for Nonroad Diesel Engines (EPA 420-F-98-034) that phase in reduction of diesel engine emissions by 66% over a ten year period.
Very specific procedures to verify regulatory compliance of new engine designs were put forward by the EPA in March 1999 in their document titled Certification Guidance for Engines Regulated Under: 40 CFR Part 86 and 40 CFR Part 89. Going through these procedures to get an engine certified are an enormous task in themselves and actually meeting these standards for EPA certification is a major accomplishment.
Over the years there has accumulated a large body of prior art that discloses a variety of approaches for providing assistance to the diesel engine combustion process. A variety of reasons have motivated these efforts, primarily to improve fuel economy, enhance engine power, and reduce pollutant emissions.
Rao et al. (U.S. Pat. No. 5,307,772) discloses a means to assist the diesel combustion process through the use of a catalyst. This catalyst is plated onto a structure that is placed between the pre-combustion chamber and the main combustion chamber in the cylinder head on a diesel engine. This catalyst-coated structure is positioned so that combusting gasses under high pressure and at high velocities must pass through it during each power stroke.
Fukano et al. (U.S. Pat. No. 5,224,449) and Ariga (U.S. Pat. Nos. 4,913,111 and 4,686,941) disclose improvements to spark-assisted diesel engines that consist of inducing turbulence to the combusting fuel-air mixture. In all three patents secondary combustion chambers are used to create the desired turbulence to enhance the mixing of the fuel and air. In addition to aiding the mixing process, the turbulence also exposes the spark on the tip of the spark plug to more of the fuel-air mixture. Although these systems may enhance combustion to some extent, the spark plug itself is only exposed to one specific point of the fuel-air mixture at any given time.
McCowen et al. (U.S. Pat. No. 5,855,192) discloses fuel-preheating elements, combustion chamber heating elements, and a heat retention element within the combustion chamber. The application of heat to the fuel and to the combustion chamber may assist the combustion process, especially during cold starting, as shown by the use of glow plugs and fuel pre-heaters in diesel engines currently in production; but there is a drawback to the introduction of additional heat into the combustion process in that it will result in greater creation of oxides of nitrogen. Another problem with this approach is the relative inefficiency of electrical resistance heating elements in terms of the power that they require, and their relatively short life in terms of total hours of operation after which they need to be replaced.
Chan (U.S. Pat. No. 5,852,999) discloses another example of creating and maintaining a spark that can be used in a spark assisted diesel engine. A two-point electrode arrangement is disclosed that is provided with a high frequency electrical current to create an electrical arc inside the combustion chamber. The main point in the disclosure by Chan is the concept of having the high frequency arc initiated while the piston in the combustion chamber is at bottom dead center of the compression stroke. This is done for the purpose of reducing the voltage needed to initiate the arc.
Casey (U.S. Pat. No. 4,111,178) and Kindermann et al. (U.S. Pat. No. 4,096,841) both disclose reciprocating 4-cycle direct injected spark ignited gasoline-fueled engines. The system disclosed consists of a fuel injector and a spark plug placed in a pre-combustion chamber with the spark timing controlled by a signal that originates in the fuel injector.
None of these references disclose an apparatus that will allow for the initiation of combustion for all of the fuel as it is injected into the combustion chamber followed by the maintenance of the combustion process to its completion in the manner described herein.